Difference between throw and throws keyword on Exception handling in Java is a popular core java interview question. Exception handling being an important part of Java programming language, complete knowledge of all keywords related to exception handling e.g. try, catch, finally, throw and throws is important. Main difference between throw and throws is in there usage and functionality. where throws is used in method signature to declare Exception possibly thrown by any method, throw is actually used to throw Exception in Java code, here is an example of both throw and throws keyword which makes iteasy to understand difference between them.

public void shutdown() throws IOException{

throw new IOException("Unable to shutdown");

}

if you see the code above, throws keyword is used to declare Exception thrown by this method shutdwon(), by looking at method signature we know that its throwing IOException. while inside method code throw keyword is actually used to throw instance of IOException. here are couple of more differences between throw and throws keyword in java:

1) You can declare multiple exception thrown by method in throws keyword by separating them in common e.g. throws IOException, ArrayIndexBoundException etc, while you can only throw one instance of exception using throw keyword e.g. throw new IOException("not able to open connection").

2) throws keyword gives a method flexibility of throwing an Exception rather than handling it. with throws keyword in method

signature a method suggesting its caller to prepare for Exception declared in throws clause, specially in case of checked Exceptionand provide sufficient handling of them. On the other hand throw keyword transfer control of execution to caller by throwing an instance of Exception. throw keyword can also be used in place of return as shown in below example:

private static boolean shutdown() {

throw new UnsupportedOperationException("Not yet implemented");

}

as in below method shutdown should return boolean but having throw in place compiler understand that this method will always throw exception .

3) throws keyword cannot be used anywhere exception method signature while throw keyword can be used inside method or static initializer block provided sufficient exception handling as shown in example.

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Can you please give an example of throw and throws, to understand difference between them better ? My understanding of throw is very limited but I know we can also use throw not just to throw exception but also to return from method or switch block.

throw keyword will throw the said exception and stops where as try catch methods will handle runtime exceptions and continues the regular flow of the program

throws keyword is used declare exceptions so that if there any exceptions ocuurring during the coding the compile willprompt us saying please handle the exceptionsimply speaking throws keyword is like an alarm!!

@Tushar, throw return the control back to the caller, acting like a break in the switch statement. In your example, if you pass 1 or 2 then they will throw Exception, since you don't have default case, nothing will happen if you pass any number other than 1 and 2.